Ischemic Stroke - causes, symptoms, diagnosis, treatment, pathology

Aug 26, 2023

Ischemic Stroke - causes, symptoms, diagnosis, treatment, pathology

What are ischemic strokes? Ischemic strokes occur when there’s a blocked artery that reduces blood flow to the brain. Find more videos at http://osms.it/more.

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Content

3.779 -> There are two main types of stroke: an ischemic stroke which is when there’s a blocked artery

8.92 -> that reduces blood flow to the brain and a hemorrhagic stroke which is when an artery

14.219 -> in the brain breaks, creating a pool of blood that damages the brain.

19.289 -> Of the two, ischemic strokes are much more common, and the amount of damage they cause

24.169 -> is related to the parts of the brain that are affected and how long the brain suffers

28.349 -> from reduced blood flow.

30.21 -> Now if symptoms self-resolve within 24 hours, it’s called a transient ischemic attack

35.85 -> and there are usually minimal long-term problems.

39.26 -> OK - let’s start with some basic brain anatomy.

42.949 -> The brain has a few regions - the most obvious is the cerebrum, which is divided into two

47.429 -> cerebral hemispheres, each of which has a cortex - an outer region - divided into four

53.23 -> lobes including the frontal lobe, parietal lobe, temporal lobe, and the occipital lobe.

59.409 -> There are also a number of additional structures - including the cerebellum, which is down

63.91 -> below, as well as the brainstem which connects to the spinal cord.

68.5 -> The right cerebrum controls muscles on the left side of your body and vice versa.

73.49 -> The frontal lobe controls movement, and executive function, which is our ability to make decisions.

79.5 -> The parietal lobe processes sensory information, which lets us locate exactly where we are

84.17 -> physically and guides movements in a three dimensional space.

88.27 -> The temporal lobe plays a role in hearing, smell, and memory, as well as visual recognition

94 -> of faces and languages.

96.149 -> Finally there’s the occipital lobe which is primarily responsible for vision.

100.26 -> The cerebellum helps with muscle coordination and balance.

103.9 -> And finally there’s the brainstem plays a vital role in functions like heart rate,

109.229 -> blood pressure, breathing, gastrointestinal function, and consciousness.

118.119 -> The brain receives blood from the left and right internal carotid arteries, as well as

122.719 -> the left and right vertebral arteries, which come together to form the basilar artery.

127.979 -> The internal carotid arteries turn into the left and right middle cerebral arteries which

132.84 -> serve the lateral portions of the frontal, parietal, and temporal lobes of the brain.

138.239 -> Each of the internal carotid arteries also give off branches called the anterior cerebral

143.319 -> arteries which serve the medial portion of the frontal and parietal lobes and connect

148.37 -> with one another with a short little connecting blood vessel called the anterior communicating

152.98 -> artery.

153.98 -> Meanwhile, the vertebral arteries and basilar artery gives off branches to supply the cerebellum

159.73 -> and the brainstem.

161.33 -> In addition, the basilar artery divides to become the right and left posterior cerebral

165.92 -> artery which mainly serve the occipital lobe and some of the temporal lobe as well as the

171.14 -> thalamus.

172.16 -> Finally, the internal carotid arteries each give off a branch called the posterior communicating

177.909 -> artery which attaches to the posterior arteries on each side.

182.97 -> So together, the main arteries and the communicating arteries complete what is called the Circle

188.37 -> of Willis - a ring where blood can circulate from one side to the other in case of a blockage.

195.62 -> The Circle of Willis offers alternative ways for blood to get around an obstructed vessel.

200.989 -> In general, the brain can get by on diminished blood flow - especially when it happens gradually

206.83 -> because that allows enough time for collateral circulation to develop, which is where a nearby

213 -> vessel starts sending out branches of blood vessels to serve an area that’s in need.

217.94 -> But once the supply of blood flow is reduced to below the needs of the tissue - it causes

222.61 -> tissue damage, which we call an ischemic stroke.

226.03 -> There are two main ways that an ischemic stroke happens.

230.19 -> One mechanism is endothelial cell dysfunction, which is when something irritates or inflames

235.79 -> the slippery inner lining of the artery—the tunica intima.

240.4 -> One classic irritant is the toxins found in tobacco which float around in the blood damaging

246.219 -> the endothelium.

250.51 -> That damage becomes a site for atherosclerosis, which is where a plaque forms.

255.489 -> This is when a buildup of fat, cholesterol, proteins, calcium, and immune cells forms

261.039 -> and starts to obstruct arterial blood flow.

263.83 -> This plaque has two parts to it, the soft cheesy-textured interior and the hard outer

269.139 -> shell which is called the fibrous cap.

274.78 -> Branch points in arteries and particularly the internal carotid and middle cerebral arteries

279.889 -> are the most common spots for atherosclerosis.

282.75 -> Usually, though, it takes years for plaque to build up, and this slow blockage only partially

288.94 -> blocks the arteries, and so even though less blood makes it to brain tissue, there’s

294.27 -> still some blood.

296.039 -> So Strokes happen when there’s a sudden and complete or near-complete blockage of

300.84 -> an artery—so let’s see how that can happen.

303.74 -> Since plaques sit in the lumen of the blood vessel, they’re constantly being stressed

307.86 -> by mechanical forces from blood flow, and interestingly it’s often the smaller plaques

312.9 -> that are more dangerous.

314.669 -> Their fibrous caps are softer than the larger ones and are prone to getting ripped off.

321.19 -> Once that happens, the inner cheesy filling is exposed to the blood and is thrombogenic,

325.919 -> which means that it tends to form clots very quickly.

329.43 -> Platelets adhere to the exposed cheesy material, and they release chemicals that enhance the

333.84 -> clotting process.

335.6 -> Within a minute that artery can be fully blocked.

341.52 -> Another mechanism for ischemic stroke formation is an embolism.

345.2 -> An embolic stroke typically happens when a blood clot breaks off from one location, travels

350.259 -> through the blood, and gets lodged in an artery downstream, typically an artery, arteriole,

356.199 -> or capillary with a smaller diameter.

359.27 -> These blood clots typically emerge from atherosclerosis, but they can also form in the heart.

367.11 -> For example stagnant blood can form a clot, and blood can stagnate due to an atrial fibrillation

372.93 -> or after a heart attack.

374.389 -> If a clot forms in the left atrium, it moves into the left ventricle and from there it

379.71 -> has a direct route to the brain.

381.79 -> On the other hand, if a clot forms in the low-pressure veins or right atrium, then it

386.94 -> goes into the right ventricle and gets lodged in the pulmonary capillaries - with no way

391.62 -> of getting to the brain.

393.819 -> An important exception is if a person has a heart defect like an atrial septal defect

398.979 -> that allows blood and potentially a blood clot to wander from the right side of the

403.69 -> heart over to the left side of the heart.

405.99 -> In that situation, a venous or right atrial blood clot will have bypassed the pulmonary

411.33 -> circulation and established a route to the brain.

417.74 -> One specific type of ischemic stroke is called a lacunar stroke, and they typically involve

422.61 -> the deep branches of the middle cerebral artery that feed the basal ganglia.

427.86 -> Lacunar refers to “lake”, and is called that since after a lacunar stroke the damaged

432.569 -> brain tissue develops fluid filled pockets called cysts that look like little lakes under

437.44 -> a microscope.

438.759 -> Lacunar strokes classically develop as a result of hyaline arteriolosclerosis which is when

444.58 -> the arteriole wall gets filled with protein.

447.87 -> This can happen as a result of hypertension or diabetes, and can make the artery wall

453.319 -> quite thick, reducing the size of the lumen.

456.8 -> In addition to problems specific to an artery, something like shock can lead to a reduction

461.5 -> in blood flow throughout the entire body.

464.629 -> In these cases, the tissues that are the furthest downstream are affected the most.

468.72 -> This is because healthy tissue continues to extract what it needs from the blood flowing

473.069 -> by, leaving little or no oxygen and nutrients for the tissue furthest away.

478.32 -> The “furthest downstream” tissues in the brain are at the border of two different blood

482.55 -> supplies.

484.479 -> When the blood flow throughout the body is diminished for any reason, they get damaged,

489.18 -> and this pattern of injury is called a watershed infarct.

495.08 -> Regardless of the mechanism of an ischemic stroke, it’s helpful to remember that there’s

499.259 -> an ischemic core, which is the brain tissue that will likely die from ischemia, and then

504.63 -> there’s tissue around the core, called the ischemic penumbra, which is preserved for

508.659 -> a period of time by collateral circulation and has a chance to survive if blood flow

513.501 -> is restored quickly enough.

518.03 -> Regardless of the type of ischemic stroke, without a steady supply of glucose and oxygen,

523.13 -> cells run out of energy within minutes and you get a high buildup of sodium and calcium

527.79 -> levels.

529.64 -> High sodium levels draws water into the cell making it swell, this is called cytotoxic

535.6 -> edema.

536.7 -> And high calcium leads to the buildup of reactive oxygen radicals that react with lipids in

541.97 -> the membranes of mitochondria and lysosomes.

545.7 -> Damage to these organelles allows apoptosis-inducing factors and degradative enzymes to seep out

551.29 -> of the cell.

554.29 -> Over a period of 4-6 hours, immune cells begin to haul away damaged cells and the resulting

559.44 -> inflammation damages the blood brain barrier allowing fluid and proteins to get into the

565.1 -> brain tissue causing swelling or vasogenic edema.

569.56 -> Because the skull creates a fixed volume the swelling leads to a mass effect where the

573.84 -> swollen brain tissue pushes into the unaffected side of the brain-called cingulate or uncal

580.1 -> herniation, or slips down and out of the base of the skull - called cerebellar tonsil herniation,

586.85 -> which is particularly dangerous because it can push onto the brainstem and affect breathing

591.45 -> and consciousness.

595.27 -> Stroke symptoms depend on the exact part of the brain that is affected.

599.23 -> For example, an anterior or middle cerebral artery stroke can cause numbness and sudden

604.41 -> muscle weakness.

605.46 -> If a stroke affects the Broca’s area, which is usually in the left frontal lobe, or Wernicke’s

610.95 -> area, which is usually in the left temporal lobe, then it can cause slurred speech or

615.6 -> difficulty understanding speech, respectively.

617.91 -> If there’s a posterior cerebral artery stroke, then it can affect vision.

624.7 -> An acronym to remember some common stroke symptoms is FAST - Facial drooping, Arm weakness,

630.77 -> Speech difficulties, and Time.

633.4 -> Time is obviously not a symptom but just a reminder to get help as quickly as possible

638.21 -> to minimize cell injury and maximize the chance of a full recovery.

644.63 -> To diagnose and confirm the location and size of an ischemic stroke, medical imaging with

649.16 -> a CT or MRI can be used.

651.72 -> Also, angiography, which uses contrast injected into the blood, can help to visualize the

658.13 -> exact location where blood flow is blocked within an artery.

662.2 -> In addition, using FLAIR sequence MRIs, it’s possible to distinguish a new stroke injury

667.9 -> from an old one.

671.5 -> In an ischemic stroke the ultimate treatment is to reestablish blood flow as quickly as

676.04 -> possible to prevent further cell death, particularly in the penumbra - every minute counts.

682.05 -> So thrombolytic enzymes, like tissue plasminogen activator or TPA, are used to activate the

688.64 -> body’s natural clot busting mechanisms, but TPA does have a time limit of when it

694.21 -> can be used.

695.51 -> Aspirin is also used to prevent platelets from forming additional clots.

700.13 -> If TPA is unsuccessful, surgical procedures can be used that push a wire through the artery

706.32 -> and physically remove the clot.

708.76 -> In mechanical embolus removal in cerebral ischemia, called MERCI for short, the wire

714.42 -> grabs on to the clot and draws it out of the artery.

717.99 -> In suction removal, the wire is used to physically break down the clot and clot fragments are

723.14 -> removed with suction.

726.54 -> After a stroke has occurred, there is an elevated risk of having additional strokes so it’s

730.95 -> important to minimize risk factors - the main one being quitting smoking, but others include

735.98 -> having a healthy blood pressure, normal LDL cholesterol levels, and controlling other

740.7 -> diseases like diabetes.

742.61 -> Occasionally, a surgery may be necessary to help clean arteries obstructed by severe atherosclerosis.

749.57 -> For example, in a carotid endarterectomy, the internal carotid artery is opened up and

754.98 -> atherosclerotic plaque is removed.

757.79 -> Alternatively, a stent may be placed to keep the artery opened up.

762.4 -> Okay, a quick recap: An ischemic stroke occurs when there’s an acute decrease in the arterial

769.16 -> blood supply.

770.5 -> It can be due to atherosclerosis, a thrombus, an embolus,, or a global reduction in blood

776.63 -> flow.

777.63 -> The goal is to identify symptoms and reestablish blood flow to prevent long-term damage - to

783.31 -> remember this a common acronym is FAST - Facial drooping, Arm weakness, Speech difficulties,

789.07 -> and Time.

Source: https://www.youtube.com/watch?v=2IgFri0B85Q